This disclosure relates to novel methods for preparing fluorinated organic compounds, and more particularly to methods of producing fluorinated hydrocarbons.
Hydrofluorocarbons (HFCs), in particular hydrofluoroalkenes or fluoroolefins, such as tetrafluoropropenes (including 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf or 1234yf)) have been disclosed to be effective refrigerants, fire extinguishants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFCs do not contain chlorine and, thus, pose no threat to the ozone layer.
In addition to ozone depleting concerns, global warming is another environmental concern in many of these applications. Thus, there is a need for compositions that meet both low ozone depletion standards as well as having low global warming potentials. Certain fluoroolefins are believed to meet both goals. Thus, there is a need for manufacturing processes that provide halogenated hydrocarbons and fluoroolefins that contain no chlorine that also have a low global warming potential.
One such HFO is 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf or 1234yf). The preparation of HFO-1234yf starting from CQ2═CCl—CH2Q or CQ3-CCl═CH2 or CQ3-CHCl—CH2Q may include three reaction steps, as follows:                (i) (CQ2=CCl—CH2Q or CQ3-CCl═CH2 or CQ3-CHCl—CH2Q)+HF→2-chloro-3,3,3-trifluoropropene (HCFO-1233xf or 1233xf)+HCl in a vapor phase reactor charged with a solid catalyst;        (ii) 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf)+HF→2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb or 244bb) in a liquid phase reactor charged with a liquid hydrofluorination catalyst; and        (iii) 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb)→2,3,3,3-tetrafluoropropene (HFO-1234yf) in a vapor phase reactor;wherein Q is independently selected from F, Cl, Br, and I, provided that at least one Q is not fluorine.        
The hydrofluorination of 1233xf to 244bb is usually conducted in the presence of fluorinated SbCl5 at temperatures above 70° C.; otherwise the catalyst will freeze. Under these conditions, the 1233xf is not completely converted to 244bb because of equilibrium limitations, especially at higher temperatures. As a result, significant amounts of 1233xf are present in the product formed. Since the boiling points of 1233xf and 244bb are only about 2° C. apart, separation of these two species is difficult and expensive.
Moreover, the presence of 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) in the reaction starting materials, such as HCFC-244bb feedstock, can lead to dramatically reduced conversion of HCFC-244bb to HFO-1234yf. In addition, the 2-chloro-3,3,3-trifluoropropene copresence in the starting material, when subjected to dehydrochlorination, can lead to the formation of trifluoropropyne and oligomers, which can produce tar. This result is disadvantageous from the standpoint of a reduced yield of the desired product. Therefore, there is a need for a better catalytic reaction to achieve a higher conversion of 1233xf to 244bb to avoid and/or minimize the need for purification.
The present invention fulfills that need.